Use of Saint John’s wort for depression may significantly decrease efficacy of anti-leukemia drug imatinib
Saint John's wort, an herb generally thought
to be a safe natural remedy for mild depression, may significantly
decrease the ability of imatinib to prevent relapse in leukemia
patients, according to a presentation at the annual meeting of the
American Society for Clinical Pharmacology and Therapeutics.
Researchers who studied healthy volunteers
to determine whether the herbal preparation interacts with imatinib
mesylate, (Gleevec R) found that taking the two agents together
caused the amount of Gleevec in the blood to drop nearly 30 percent.
Patients with chronic myelogenous leukemia,
an aggressive disease, who go into remission must continue to take
daily oral doses of imatinib to prevent a recurrence. Reginald F.
Frye, PhD, the study presenter, said "A 30 percent decrease
in the level of Gleevec is significant to cancer patients. It is
the same as lowering the dose - which is enough to allow for a relapse
in the cancer growth."
"The emergence of studies such as this
shows the need for health-care professionals to have current scientific
information on the safety and efficacy of natural supplements,"
said Veronika Butterweck, Ph.D.
Patients should be aware that any product they take, whether herbal,
nonprescription or prescription, has the potential to alter how
their body handles other drugs they are taking, added study collaborator
Merrill J. Egorin, MD. "The interactions of herbal preparations
and even certain foods can be an important factor in how well a
patient may absorb or metabolize certain drugs, and those differences
can have important clinical consequences," Egorin said.
The first indication that the herb interacts with other medications
came after physicians noted drugs designed to prevent organ rejection
weren't as effective in transplant patients who were taking it.
A few years ago, the U.S. Food and Drug Administration issued a
public health advisory after federal research showed St. John's
wort interferes with medicines used to treat patients with HIV.
Those findings raised concerns that the herb also might interact
with drugs taken by patients with heart disease, depression or seizures.
In the current study, 12 healthy, nonsmoking
volunteers, six men and six women, took one 400-milligram dose of
imatinib. Researchers then took a series of blood samples over a
72-hour period to see how much of the drug had been metabolized.
For two weeks after the blood tests, study participants took 300
milligrams of St. John's wort three times each day. On the 15th
day, they again were given one dose of imatinib mesylate, and the
blood tests were repeated to measure drug levels.
Frye noted a marked decrease of imatinib
in the subjects' bloodstreams after they took the St. John's wort
regimen, indicating the herbal product caused the body to metabolize
the medicine at a faster rate, weakening its effectiveness. He urged
patients to meticulously report every supplement to their doctors
when asked about other medications.
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